“Almost every statement has a built-in defense,” said the Air Force’s chief prosecutor, Col. Don Christensen. “ ‘I did have sex with her, but I thought she was consenting.’ We rarely get confessions in a sexual assault case.”

Nevertheless, aggressive measures the Air Force has adopted to prosecute sexual assaults seem to be showing results with more cases — and more difficult cases — being prosecuted. Last year, the Air Force alone prosecuted more cases than all the services combined reported prosecuting just six years earlier.

That’s no easy task. A typical sexual assault case is among the most difficult crimes to successfully prosecute, litigators say.

Many victims don’t report the assault for days or longer, because of humiliation, fear or privacy concerns.

Many victims have hazy memories because of the neurological effects of trauma and alcohol, lapses defense lawyers argue show lack of credibility.

And many people believe that if a woman was forced into sex by an acquaintance after getting drunk, or awoke to find a man assaulting her, it was her fault for allowing herself to become vulnerable, or that she had likely consented, then regretted it, then lied about it.

Yet the Air Force prosecuted 96 sexual assault cases last year, including 15 cases in which civilian jurisdictions where the off-base assaults occurred declined the cases as unwinnable. Of those 15, “so far, we have eight convictions,” Christensen said. “We don’t shy away from a tough case.”

By contrast, in 2006, all the services combined reported 72 sexual assault prosecutions, according to the first of what is now an annual — and increasingly comprehensive — Defense Department report on sexual assault.

After decades of ignoring sexual assault in the ranks, the Defense Department, prompted by Congress after numerous, high-profile sexual assault scandals, has spent the past seven years and increasing millions of dollars trying to address the issue.

According to widely held public perception, those efforts have yielded little, as a spotlight on military sexual assault continues in the wake of recent scandals and studies:

Despite all that, it seems clear that a part of the military effort — to prosecute sexual offenders — is rapidly gaining traction, particularly in the Air Force.

“It does seem that there are far more cases being taken to trial, including cases you’d never see in civilian court,” said psychologist David Lisak, an expert on sexual violence and a forensic consultant to the military, universities and law enforcement. “I really hope, and I’m beginning to believe, we are seeing the fruits of sustained training.”

Defense lawyers who represent troops accused of sexual assault agree that the prosecution rate has vastly increased, though they question the motives.

“There are a lot of nonmeritorious cases being brought because no one wants to tell the accuser or the accuser’s parents that there’s no ‘there’ there,” said Neal Puckett, a former Marine lawyer and judge who now represents servicemembers — many of them for sexual assault — in private practice.

“I think that the pendulum has swung towards, if someone makes an allegation, she has her day in court. I’ve got to tell you, this whole concept that the system is broken (for victims) is a flawed proposition.”

“We get the right people, make sure they’re properly trained,” he said. Formerly, they spent three years in the position; now it’s four.

In especially notable or tough cases, Christensen, an Air Force lawyer with 21 years of litigation experience, details himself to prosecute.

One of those cases involved a high-ranking officer accused in March of groping a sleeping houseguest after an impromptu party at his house. Lt. Col. James Wilkerson, as the inspector general for the 31st Fighter Wing at Aviano Air Base, an F-16 pilot and close friend of the vice wing commander, held a privileged position. His accuser, a civilian physician’s assistant new to the base, did not.

She, like everyone else at the party, had been drinking. Wilkerson, and his wife, denied that any assault had occurred.

The case might not have gone to trial a few years ago. But in November, Wilkerson was convicted by an all-male jury of aggravated sexual assault, sentenced to a year in jail and dismissed from the service.

It was the fourth sexual assault prosecuted at Aviano in 2012, and the fourth conviction. The Air Force now posts online a 37-page report of sexual assault cases in which its prosecutors have won convictions over the past two years, naming defendants and their bases, and detailing charges and sentences in more than 40 cases. That would have been unthinkable a decade ago.

Lisak said the military now does more to deal with sexual assault than other segments of society.

According to the National Institute of Justice, studies indicate that between 18 percent and 20 percent of college women are raped or otherwise sexually assaulted during their college years. Collegiate victims “face a depressing array of barriers that often assure their silence or leave them feeling victimized a second time, according to a 2010 report by the Center for Public Integrity, while perpetrators “can face little or no punishment ... as colleges and universities ignore the problem.”

Last year, the National Intimate Partner and Sexual Violence Survey found that nearly one in five U.S. women had experienced rape or attempted rape at some point. According to the Bureau of Justice Statistics, 65 percent of such victims do not report to police.

In 2010, the Defense Department took 21 percent of reported sexual assault cases to trial, a “dismal” record, according to a New York Times editorial.

According to an estimate from the Rape, Abuse and Incest National Network, just nine of 46 assaults reported to police are prosecuted, or 19.5 percent.

“What frustrates me is a comparison to some imaginary place where sexual assaults are handled well,” Lisak said. “That’s a fantasy. There is no such place. Frankly, there’s far less being done to correct the problem in the civilian world.”

Until 2005, the military didn’t keep statistics on sexual assault, which meant it was impossible even to measure the problem, let alone address it.

Commanders often did not pursue criminal charges against accused offenders, whose careers proceeded unfettered, and frequently punished victims for “collateral misconduct,” such as underage drinking or fraternization.

That’s changing.

“A commander who is believed to turn a blind eye to (sexual assault), his career will be derailed,” Christensen said.

Air Force lawyers, investigators and higher commanders, including those with court-martial convening authority, now become informed of potential cases early on. “It’s never done in a command vacuum,” Christensen said.

Last year, Defense Secretary Leon Panetta ordered that unit commanders were no longer to make the decision on how to handle sexual assault complaints, giving that responsibility to higher level commanders.

Victims’ advocates and some legislators say that sexual assault complaints should be handled outside the chain of command. Even higher-level commanders can’t be trusted to bring prosecutions when the spotlight fades, they say.

“You’re not going to fix the rape problem if you allow people that are openly sexist and mocking of women to be the ones victims report to,” said Susan Burke, a lawyer who represents military women in sexual assault or harassment lawsuits against the Pentagon.

Panetta also ordered that more special victims investigators and prosecutors be trained and assigned, an effort still in the works. Victims also are newly able to request a transfer to another base.

The victim in the Wilkerson case at Aviano knew that her report would be sent to Wilkerson’s friend, the vice-wing commander, who had also been at the party at Wilkerson’s house and was dating a friend of hers. It was “awkward,” she said in an interview after the trial and sentencing.

The investigation into her case led to charges against Wilkerson — and the vice-wing commander being fired from that position and transferred to the Pentagon. The woman still works at Aviano and said she’s content there.

Being assaulted and going through an intrusive criminal justice process had been a terrible ordeal, she said, but she’d felt a lot of support from victim advocates, her military boss, investigators and prosecutors.

“I wonder if this had happened in the civilian sector whether I’d have gotten the same support,” she said.